1. Field of the Invention
The present invention relates to a flash device and a camera having the flash device.
2. Description of Related Art
It has recently become popular to incorporate an electronic flash device into a camera for the purpose of a reduction in size of a camera system. With regard to the camera body, it has become a general trend to equip cameras with zoom lenses instead of conventional fixed-focus lenses.
As a result, cameras of these days permit taking an enlarged picture of an object of shooting located far away, by setting the zoom lens at a telephoto position where it has a long focal length. Meanwhile, the magnification rate of a lens has advanced to make the F-number which indicates the brightness of the lens on the telephoto side larger. The larger F-number so to say indicates a darker lens. The darker lens requires a flash device to be arranged to have greater light emission energy.
Such being the situation, a built-in flash device which is incorporated in a camera is generally arranged to require a large amount of flash-device charging energy and a large main-capacitor discharging energy for each shot of flash photography. On the other hand, however, a general desire for reduction in size of cameras urges use of a smaller power supply battery. As a result, the battery has come to have a smaller capacity.
However, it is deemed to be prerequisite to a flash device to have a high charging speed. Therefore, a charging circuit which charges a main capacitor by boosting the voltage of a battery is generally arranged to derive large energy from the power supply battery by raising the turn ratio of a transformer according to the so-called forward converter method.
The flash device having such a charging circuit is, however, inferior in the efficiency of use of energy of the battery. Therefore, under the requirement for a reduction in size of the battery and an increase in charging and discharging energy, it has been desired to enhance the efficiency of use of the battery energy in charging the main capacitor.
It is an object of the invention to provide a flash device arranged to enhance the efficiency of use of battery energy for charging a main capacitor thereof, and also a camera having the flash device.
To attain the above object, in accordance with an aspect of the invention, there is provided a control circuit for a flash device having a main capacitor, a charging circuit having a flyback-type boosting circuit and a forward-type boosting circuit which differ in characteristic from each other and arranged to charge the main capacitor by boosting a voltage of a battery with one of the flyback-type boosting circuit and the forward-type boosting circuit, and a flash discharge tube arranged to emit flash light by discharging electric charge charged in the main capacitor, the control circuit comprising a detecting circuit which detects a charged state of the main capacitor, and a selection circuit which selectively causes one of the flyback-type boosting circuit and the forward-type boosting circuit to act, on the basis of a result of detection provided by the detecting circuit.
In accordance with another aspect of the invention, in a flash device having a charging circuit which performs a boosting action on a battery voltage in a flyback-type manner and in a forward-type manner, and a capacitor arranged to be charged by the charging circuit, the boosting action is performed in the flyback-type manner at the time of beginning of charging the capacitor.
In accordance with a further aspect of the invention, in a flash device having a charging circuit which performs a boosting action on a battery voltage in a flyback-type manner and in a forward-type manner, and a capacitor arranged to be charged by the charging circuit, the boosting action is set to one of the flyback-type manner and the forward-type manner according to a charged voltage state of the capacitor.
The above and further objects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings.